Proof of Gravity and the Cavendish Experiment

The Earth is not those two iron spheres, and thus shouldn't be expected to share the same properties.

Why not? Even in the FE model, the Earth is composed largely of metals.

http://www.theflatearthsociety.org/forums/viewtopic.php?t=1361&highlight=magnetic+field

Edit: I know Erasmus never says "metallic magnets" in the above explanation, but I think it's a fair assumption.  I take it he isn't referring to super conductors, so the magnets must be metallic.

But even that isn't necessary. Would performing this experiment with two massive rocks (Parts of the Earth) convince you that the Earth has gravity?

Why not? Even in the FE model, the Earth is composed largely of metals.

Are you willing to test every single one of them? Otherwise the experiment only proves that iron has gravitational attraction.

But even that isn't necessary. Would performing this experiment with two massive rocks (Parts of the Earth) convince you that the Earth has gravity?

Yes. Or rather, it would show that the material making up the crust of Earth has a gravitational field.

Quote from: "Max Fagin"

Quote

But even that isn't necessary. Would performing this experiment with two massive rocks (Parts of the Earth) convince you that the Earth has gravity?

Yes. Or rather, it would show that the material making up the crust of Earth has a gravitational field.

Great.  Here is a description of an experiment that measured the gravitational atraction of several materials:

http://www.fourmilab.ch/gravitation/foobar/

and here are the timelapse videos showing the results with two chunks of rock.

http://www.fourmilab.ch/gravitation/foobar/figures/movie-3.mpg
http://www.fourmilab.ch/gravitation/foobar/figures/movie-4.mpg

Check and mate!

Great.  Here is a description of an experiment that measured the gravitational atraction of several materials:

http://www.fourmilab.ch/gravitation/foobar/

and here are the timelapse videos showing the results with two chunks of rock.

http://www.fourmilab.ch/gravitation/foobar/figures/movie-3.mpg
http://www.fourmilab.ch/gravitation/foobar/figures/movie-4.mpg

From the link on Wiki about this experiment:

Bending Spacetime in the Basement (do-it-yourself Cavendish apparatus - appears to be seriously flawed)

And there is still the question as to whether Cavendish confirms your view of gravity which must show that the experiment works with materials such as lead (or something like plastic or anything that one would presume to have minimal magnetic draw) and then still prove that with respect to such materials their effect upon a suspended object (if they have one) is not magnetism.

If it could be demonstrated that the experiment works with a variety of nonmagnetic materials, would you accept the universality of gravitation?

Great.  Here is a description of an experiment that measured the gravitational attraction of several materials:

Well the videos are, like pictures, not admissible as evidence. I'd have to be able to test it myself, and I can't use an experiment whose validity is in doubt.
Of course, anyone can edit wikipedia, so that's not reason to discount the experiment entirely. Maybe Erasmus, Engineer, or Skeptical can vouch for it?

Actually EnragedPenguin, I found this experiment so interesting, that a friend and I decided to try it out.  I'll post any videos as soon as I have them.  Are you willing to belive that I am not part of the conspiracy?

Well the videos are, like pictures, not admissible as evidence. I'd have to be able to test it myself, and I can't use an experiment whose validity is in doubt.
Of course, anyone can edit wikipedia, so that's not reason to discount the experiment entirely. Maybe Erasmus, Engineer, or Skeptical can vouch for it?

The "Discussion" section on that WP article describes the flaw in the experiment.  These calculations could probably be reproduced by the people you listed.

The "Discussion" section on that WP article describes the flaw in the experiment.  These calculations could probably be reproduced by the people you listed.

After some head scratching I came up with a differential equation describing the motion of the torsion balance arm.  Assuming there is no torque from the suspending string, no atmosphere, and a massless arm, the dynamics are:

d²θ     GM  (    cos θ/2            sin θ/2      )
---- = -----  ( --------------  -  ---------------- )
dt²      2R³  ( 1 - cos θ/2     1 + cos θ/2 )


where G is the gravitational constant, M is the mass of each fixed weight, and 2R is the distance along the balance arm at which the smaller masses are placed.

I couldn't find an analytical solution to this equation, but a numerical simulation showed that, starting from an angle of θ=10°, it took just over ten minutes for the arm to complete its motion (I used values of M and R from the website).

I am running the simulation on a greater variety of initial states, and report results when I have them.  For now, however, it would appear that it is entirely possible that Bending Spacetime in the Basement could be a genuine demonstration of gravitational attraction between two small objects.

Results of my wasted Sunday afternoon:



Estimate for yourself the initial angle and the time the arm took to complete the swing by watching the video, and decide whether it's plausible.

I will say, you are dedicated.

I see less than 5 minutes to swing through about 40 degrees.  By your kinematics, that should take a little over 80 minutes.